This invention relates to a magnetoresistor integrated sensor for measuring voltage or current, such as gigantic magnetoresistors or tunnel magnetoresistors with considerable galvanic isolation, with the sensor comprising first and second terminals for connection to a generator for which the voltage or current is to be measured, the sensor connected to a metal measuring line through which flows a current proportional to the voltage or current of the generator which is to be measured, with said current flowing through this line creating a magnetic field measured remotely by the magnetoresistors.
This invention also relates to a diagnostic system for measuring the voltage or current of a power generator which can, among other uses, be carried on-board a vehicle for a dynamic application or be arranged in a static power generation facility and which may include multiple cells.
The invention applies in part to measuring the voltage of on-board power generators comprising multiple elementary cells such as fuel cells for automotive applications.
The domain to which this invention relates is the one of on-board electronic systems for reading, processing and transmitting of the measurement of multiple voltage sources operating in a severe environment. Further, the regulatory and safety requirements for an automotive application impose a galvanic isolation of 1500 V between the unit of measurement and the source to be measured, with the galvanic isolation level being more generally defined by 2*U+1000 V RMS where U is the maximum operating voltage.
This technological need to measure multiple voltages has already been shown in patent document FR 2 934 419 A1. The technological solution shown in this prior art document is based on a principle of voltage/frequency conversion and the transmission of a binary signal through optocouplers ensuring the required galvanic isolation. However, this type of device requires a specific feed to ensure measurement. According to this document, the energy is directly drawn from the bipolar plates of the hydrogen and oxygen fed fuel cell.
In fact, various systems are known in which voltage measurements are conducted using intrusive devices that are used during the adjustment phase of the fuel cells. In this case, no on-board feed, nor measurement module are necessary since such devices do not permit performing a permanent diagnosis that interacts with the control/command of the fuel cell system for instance. In addition, for batteries that have a large number of cells, this means the presence of rather constraining cables for the environment of the battery and the use of intermediate boxes or of complex commercial or dedicated acquisition cards, for maintaining proper isolation between the battery and the measuring bench.
For the systems housed in the vehicle, the use of an on-board electronic system is known using mainly an analog-digital converter and an associated microcontroller to read, possibly to make a diagnosis and to transmit the digital data. In general, the galvanic isolation is controlled (>1500 V). The system is fed by a DC-to-DC converter and the transmission of the data passes through an optoelectronic converter. This system, made up of a converter and a microcontroller, permits reading several multiplexed cells on the converter channel or channels, referenced to one and the same potential. This reading can be direct when the battery only consists of a small number of cells and as long as the voltage of the last cell remains compatible with the voltage supplied by the DC-to-DC converter. This is no longer the case when the number of cells becomes large. Then, the voltages of the various cells must be brought back by a resistor bridge to levels compatible with the features of the converter and manage numerous multiplexers with the inherent risk of channeling a large amount of information (presence of numerous potentials in the routing, crosstalk, accuracy, switching, . . . ).
The use of several DC-to-DC converters is also known from a source external to the battery (battery, feed, . . . ) in order to supply several feed sources of the parallel managed autonomous diagnostic systems. This method permits having several references available and regrouping the cells in packages each associated with a converter and a microcontroller. Such systems are heavily penalized by the size and the complexity of processing information.
The above systems are not fully satisfactory when one considers applications where the volume and reliability constraints become overwhelming, such as in the case of an automotive application that implies the following constraints among others:                Limited space,        Heat dissipation of the various modules,        Accuracy of the measurement of the voltages for each cell that may be affected by the presence of dividing bridges and switches used to measure voltages that are sometimes weak and fluctuating,        Reliability of the measurement during the life of the vehicle, in spite of the component aging;        Compatibility of the principles of measurements and conditioning of the data with the CAN (“Controller Area Network”) network of the vehicle.        
In addition, the development of magnetoresistive sensors using giant magnetoresistors (GMR) or tunnel magnetoresistors (TMR) has been the object of intensive developments worldwide. The first application is the hard disks reading heads which are now manufactured with the help of this technology. The other applications are more recent and cover mainly position or angle sensors.
Recently, the NVE company (www.nve.com) launched the marketing of a current sensor consisting of a GMR bridge and a current line.
The Pannetier-Lecoeur, M.; Fermon, C; de Vismes, A, et al publication, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 316, pages E246-E248 (2007) which describes a GMR current sensor is also a relevant reference.
The tunnel magnetoresistors (TMR) show not only a greater sensitivity than the giant magnetoresistors (GMR) but also more noise and a more difficult manufacturing process. They can be used beneficially in the case where operating temperatures must exceed 180° C.